staging: unisys: visorbus: clean up initializations

Don't compute value of offset during initialization. Assigning a value to
offset should happen after we have verified all of its components.

Signed-off-by: David Kershner <david.kershner@unisys.com>
Reviewed-by: Tim Sell <timothy.sell@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>